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Boom, and You're Back!

Discussing why people with PTSD have intrusive memories

This is Part I in a two-part series on PTSD and intrusive memories. Next article: PTSD and Tetris

Post-traumatic stress disorder (PTSD) is an anxiety disorder which may develop if a person has been involved in or witnessed a stressful event. Whilst most people associate PTSD with soldiers, it also develops in people like you and me. In fact, many events that lead to PTSD development occur in everyday life, such as car crashes, traumatic childbirth, assaults, robberies etc.

One of the main symptoms of PTSD is intrusive memories. This is when people involuntarily develop recollections of the event within their consciousness.

Dual modality theory

The main model which explains the development of intrusive memories in PTSD is the Dual Representation Theory. This idea suggests that there are two separate memory systems which encode information during an event.

The verbally accessible memory system (VAM) holds information about the conscious experience of the event meaning it can be voluntarily recalled afterwards. This is compared to the situationally accessible memory system (SAM) which processes unconscious sensory information, like smells and sounds, which cannot be voluntarily recalled.

The theory suggests VAM is impaired and focuses on the frightening information and the fear that we experience during an event, and this effects how we process the information. Coupled with the vivid sensory information captured by SAM, when individuals are in a context where physical or sensory features are like the traumatic event, they unconsciously trigger intrusive memories which are highly distressing and emotionally valanced.

Think of the last movie you watched about someone returning from war who was scared of fireworks. Now you understand that the banging sound triggers the highly emotional memories from the SAM and VAM system, forcing them to re-witness situations where a bomb has gone off. One loud boom and they are back in a war zone.

Where in the brain is this going on?

There are many brain areas involved in PTSD memory processing, but some common areas are associated with the formation and retrieval of traumatic memories.

Hippocampus: combines lots of information in the environment into one memory that can be consciously retrieved. It seems likely that this area is essential for creating verbally accessible memories in trauma, so is part of the VAM system.

Ventromedial prefrontal cortex: involved in regulating how much emotion is encoded into a memory. It has been said that dysfunction in this area is why people with PTSD have difficulties processing the emotion attached to the traumatic event.

Amygdala: Important in how we learn to associate stimuli with the correct emotional response. It has been said in highly stressful events the amygdala becomes hyperactive which is why there is such a strong emotional reaction to certain cues, therefore is likely to be crucial in the SAM system.

Hormones: elevated levels of glucocorticoids, cortisol, and norepinephrine can influence the consolidation of memories which creates stronger and more persistent traumatic memories.

Written by Alice Jayne Greenan

Related articles: Synaptic plasticity / Can you erase your memory?

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